Wednesday, December 10, 2014

Entamoeba histolytica: A Dangerous Stowaway

Figure 1: A histological slide of amoeba infected brain
tissue.The left side of the image shows
a trophozite that has disseminatedto the brain tissue. The smaller darker spots in are amoebic cyststhat have formed in the brain tissue.

Amebiasis
is an infection of the intestines that is caused by the parasite Entamoeba
histolytica.This parasitic amoeba infects
the host through the fecal-oral rout.However the parasite
may spread and infect other organs such as the liver and, or the brain.Infection of the brain can be fatal (figure
1 [1]). Infection by E. histolytica happens when the host 1).
Ingests a mature cyst containing the parasite, found in food, water, or
on unwashed hands that are contaminated with fecal matter. 2).
Excystation of the mature cyst (where
the parasite escapes from the cyst) occurs in the small intestine. 3).
Trophozoites (the active and motile stage of the parasite) are then
released and migrate to the large intestine. The trophozoites multiply by
binary fission and produce cysts. 4). These cysts are then passed in the
feces of the host. Because of the
protection conferred by their walls, the cysts can survive days to weeks in the
external environment and are responsible for transmission. Trophozites can also be transmitted through
fecal matter as well, but do not last long in the environment and are destroyed
quickly. (Figure 2 [2]).

Figure
2: A
diagram of E. histolytica life cycle
in the human body,including possible sites where the parasite can disseminate
to cause disease.

However
In many cases the trophozoites remain confined to the intestinal lumen of
individuals who are thus asymptomatic carriers, and cyst passers. This is a
non-invasive infection. In some patients
the trophozoites invade the intestinal mucosa and cause intestinal disease,
like colitis.The parasites can also
disseminate in the body through the bloodstream, invading extra-intestinal
sites such as the liver, brain, and lungs causing extra-intestinal
disease.The result of which can lead to
sever pain in certain regions of the body, liver abscess, high fever, and even
death. Transmission can also occur during sexual contact, in which not only
cysts, but also trophozoites can be transmitted. All sexually active individuals who practice
unsafe oral-anal sex, and immunocompromised individuals are at an increased
risk for contracting an E. histolytica infection.

In a study by Salit et al. researchers found a cluster of E.
histolytica infectionsin Canada.They traced this cluster to several
individuals. Patient A who is a female, patient
B who is a female, and patient C who is a male, had all recently traveled to
England, Germany and Southern Italy together and returned on September 2007.Five months later patient A developed
anorexia, chills, a fever of 39.5º C, and abdominal pain.After being admitted to the hospital, she was
found to have a liver abscess (an accumulation of puss) and colitis
(inflammation of the intestines).After
several tests, it was discovered that she had been infected with a highly
virulent strain of E. histolytica that
had disseminated and caused her liver abscess.Three months after, patient C was also found to have two liver abscesses
in the same part of the liver as patient A.The tests concluded that he too was infected with the same highly
virulent strain of E. histolytica.Patient
B was infected with the same strain as well, and had developed
lymphadenopathy (refers to enlarged lymph nodes).

The researchers found that all
three of these patients had been sexually active together, and had other sexual
partners who were labeled patients D, F, and G.Patient A had another sexual partner, patient E, who also was diagnosed
with a liver abscess and intestinal colitis as well. Patients D, F, and G were female homosexuals
and bisexuals who were sexually linked to patients A, B, and C.They all reported engaging in oral-anal
sexual activity.Patients D, F, and G
were also found to be infected with E. histolytica but they did not show
any symptoms.It was concluded that
although patient E did in fact travel to Iraq and Africa, it was most likely
that he contracted the infection from engaging in sexual activity with patient
A. [5] These cases are an example of how this parasite can be very easily
transmitted from one person to another.The patients in this study all practiced oral-anal sex with each other,
which lead to an increased chance of contracting the parasite from the infected
partner.

It is known that individuals with
compromised immune system; are more often infected with common microorganisms
that would usually not be deadly, individuals infected with HIV-1 for
example.However a recent study by
Nagata et al. had some interesting finding when comparing risk factors for
amebiasis infections.They conducted a
study on 10,930 patients infected with amebic colitis over a span of seven
years. They studied the infection pattern
in Japan from 2003 to 2009 they found that there was a significant increase in
the number of infections in this time span.They performed endoscopic tests on all the patients at that time and
confirmed amebic colitis.The researchers
found that in 2003 there were about 3 out of every 1,904 patients that had tested
positive for amebic colitis, whereas in 2009 there were 12 in every 1,360
patients that had tested positive.That
is a 5.6-fold increase in the number of cases of colitis related to amebic
infections in the span of seven years.

The researchers assessed the risk
factors associated with this jump in infections, and concluded that were
several factors that can be traced back to individuals who were HIV-1 positive,
individuals who had a history of syphilis, and individuals who were sexual
activity with commercial sex worker (CSWs).However when they investigated further into the HIV-1 risk factor, they
found that there was no association with the infection itself and being HIV-1
positive, rather it was the risky behavior that these individuals engaged in
that led to their higher rate of infection. [4]

Amebiasis
is a serious condition that is caused by Entamoeba histolytica.It is not a major cause for concern in
most industrialized countries.However
when contracted it can be dangerous and sometimes fatal if not treated
quickly.It can cause liver abscess,
colitis, and if disseminated to the brain can cause death.Everybody can get this infection, although
sexually active individuals, especially those individuals who practice unsafe oral-anal
sex, have to be cautious and take enteric precautions (precautions against
possible contamination from bodily fluids of the gastrointestinal (GI) tract of
a person suspected of having a GI infection) to keep from getting infected with
this parasite.Also immunosuppressed individuals
have to be careful of this infection, as well as people who do not have access
to adequate hygiene or a clean water source.

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